1. Field of the Invention
The present invention relates to a film unit for use in diffusion transfer color photography and, more particularly, it relates to a diffusion transfer color photographic film unit which can be imagewise exposed in a camera and can be processed in a bright place outside the camera while permitting the formation of the image to be observed.
2. Description of the Prior Art
The so-called diffusion transfer color photography, in which a silver halide emulsion is used as a light-sensitive element and imagewise distributed diffusible dyes are formed as a result of the development of exposed silver halide grains and are allowed to diffuse into another hydrophilic colloidal layer followed by fixation, has the advantage that, since dye images are formed in a place remote from where silver deposits and residual silver halide exist, after-treatments such as fixing and bleaching are not necessary and color images can be obtained by only one developing step. Furthermore, a film unit which, after imagewise exposure in a camera and subsequent contact with a processing composition, can immediately be withdrawn from the camera with the light-sensitive element being maintained in a light-intercepting state and can be processed in a bright place, and a film unit which enables the observation of the degree of the formation of the diffusion transfer image in a bright place and which can be stored without separating an image-receiving layer have been suggested.
In film units as described in U.S. Pat. Nos. 3,415,644, 3,573,043 and 3,615,421, the images are formed on the same side as the side exposed in a camera. An image-inverting optical system must be used with these film units to obtain photographic images which are not inverted. Therefore, the structure of the camera is special and complicated, and special considerations on maintaining the accuracy of the focus are required.
On the other hand, film units having a structure in which photographic images are formed on the back side of the surface exposed are advantageous in that these units can be employed with cameras of the commonly used type. However, with the film units of this type, both sides of the light-sensitive element must be shielded from light during processing. The opposite surface of the light-sensitive element to that to be exposed can be shielded from light by covering the surface with a processing solution permeable layer containing carbon or a like light absorbent, whereas the surface of the light-sensitive element to be imagewise exposed needs such means which does not diffuse or absorb light during imagewise exposure but which, during processing in a bright place, can completely intercept intense light. One example of a means for intercepting light so that it does not reach the exposed surface of the film unit upon processing is a light-intercepting sheet attached to one end of the film unit, as illustrated in U.S. Pat. Nos. 3,415,645 and 3,415,646. During imagewise exposure, this sheet is turned over from the surface to be exposed and, upon the distribution of the processing solution, it is superposed on the exposed surface to cover the exposed surface. However, the movement of a light-intercepting sheet in a camera imposes many technical difficulties, for example, a large space is required inside the camera, the mechanism of the camera is complicated and the structure of the cassette retaining a film unit is complicated.
Another example of a means for intercepting light so that it does not reach the exposed surface of a film unit is an approach in which a processing solution containing a light absorbent is spread on the exposed surface of a light-sensitive element, as illustrated in U.S. Pat. No. 3,635,707. However, this method cannot be applied to the stratum structure to be used in the present invention in which an image-receiving element and a light-sensitive element are coated on different transparent supports, although it can be applied to a film unit having a stratum structure in which the image-receiving element and the light-sensitive element are coated, one over the other, on the same support.